The present invention relates to an improved butterfly valve construction.
By way of background, while there have been teachings in the past of the use of fluid pressure to aid in valve seating, such as shown in prior U.S. Pat. No. 2,973,181, issued to J. R. Johnson and U.S. Pat. No. Re. 24,102, the valves of such patents were of entirely different construction and mode of operation in that they were not butterfly valves such as shown in the present invention. Furthermore, in copending application Ser. No. 775,517, now U.S. Pat. No. 4,133,512, dated Jan. 9, 1979, slight expansion of the seating member could occur at low pressures, and this could result in undesirable leakage. The present invention is concerned with preventing such undesirable expansion of the seating member.